The present invention relates generally to an insulating layer film formed on a substrate of a semiconductor device, and particularly to a dielectric film with a multilayer nanolaminate structure consisting of a boron nitride thin film and a silicon nitride thin film capable of improving the properties of a wet etching and lowering a dielectric constant. More particularly, the present invention relates to a method for depositing the multi-layer nanolaminate thin film using an atomic layer deposition (ALD) process.
A boron nitride (BN) thin film has a low dielectric constant in a range of from about 2.2 to 5, according to the deposition conditions. The dielectric constant of a silicon nitride (SiNx) thin film, on the other hand, is about 7. Accordingly, when BN and SiNx thin films are used together, the capacitance of the BN thin film is decreased in comparison with that of the SiNx thin film causing a reduction in the propagation delay. At the same time, the properties of a BN thin film in dielectric film applications include an excellent mechanical resistance against chemical mechanical polishing (CMP) slurries and an excellent selective rate of a reactive ion etching (RIE) for a silicon dioxide layer (SiO2) and a silicon nitride layer (Si3N4). Therefore, in semiconductor technology, there is increasing interest in the use of a BN thin film that is used as the low dielectric material and CMP-stop layer.
However, applications for the use of BN thin films is limited by such factors as an adhesive failure between the BN thin film and the corresponding underlying layer of the semiconductor and an out-diffusion of the boron from the BN thin film during the annealing step, because the BN thin film lacks chemical stability at elevated temperatures.
Also, most of the conventional BN thin films were deficient in the lack of step coverage properties when formed by plasma enhanced chemical vapor deposition (PECVD) processes.
Recently, atomic layer deposition (ALD) processes have been applied to the deposition of BN thin films to achieve excellent step coverage properties and uniformity, and to deposit a conformal stoichiometric boron nitride thin film at relatively low temperatures between about 200xc2x0 C. and 250xc2x0 C.
However, BN thin films deposited by ALD methods as described above still have performance problems, such as the fact that such films are apt to decompose by moisture in the atmosphere and are easily etched during high temperature wet chemical processing. Also, BN thin films deposited by ALD processes have typically demonstrated poor oxidation resistance.
To solve the problems as described above, a general object of the present invention is to provide insulating layers for semiconductor devices with a multi-layer nanolaminate structure consisting of SiNx/BN thin films, together with methods for forming such insulating layers so as to improve etching properties when using high temperature wet chemical processing and to lower the dielectric constant.
A further object of the invention is to provide insulating layers for semiconductor devices having a multi-layer nanolaminate structure consisting of alternating SiNx/BN thin films, and methods for forming such insulating layers which prevent or minimize out diffusion of boron from the BN thin film during processing.
In accordance with one aspect of this invention, the invention provides an insulating layer in a semiconductor device with a multi-layer nanolaminate structure wherein silicon nitride thin films and boron nitride thin films are alternately formed on a surface of a wafer.
A thickness of the silicon nitride thin films according to this invention is more than that of a monolayer of the silicon nitride thin film but also less than about 200 xc3x85. A thickness of the boron nitride thin films according to this invention is more than that of a monolayer of the boron nitride thin film but also less than about 200 xc3x85. In the multi-layer nanolaminate structures of this invention, the silicon nitride thin film preferably constitutes a bottom layer of the structure or both the top and bottom layers.
Furthermore, a preferred method for forming an insulating layer in a semiconductor device according to the present invention comprises the sequential steps of: forming a silicon nitride thin film on a wafer; forming a boron nitride thin film on the previously formed silicon nitride thin film; and then forming the remainder of a multi-layer nanolaminate thin film by alternately repeating the process for forming the silicon nitride thin film and the process for forming the boron nitride thin film until the desired number of alternating silicon nitride and boron nitride thin film layers has been deposited.
The processes of forming the silicon nitride thin film and the boron nitride thin film are repeated on the wafer in a desired number of depositing cycles in-situ, preferably between about 25-35 times and 35-45 times, respectively, using the ALD method. This thin film deposition process may be carried out at a wafer temperature of about 400xc2x0 C. to 600xc2x0 C. and at a deposition pressure of about 1 to 3 torr.
The depositing cycle or process for forming each silicon nitride thin film layer comprises the sequential steps of: introducing a first silicon nitride process gas containing Si to a chamber containing the wafer to be adsorbed on a surface of the wafer; introducing a second silicon nitride process gas to purge the chamber and to exhaust any of the first silicon nitride process gas that remains unadsorbed; introducing a third silicon nitride process gas containing a reactive nitrogen entity to the chamber to react with the portion of the first silicon nitride process gas that was adsorbed on the surface of the wafer, and, introducing a fourth silicon nitride process gas to purge the chamber and to exhaust any of the third silicon nitride process gas that remains unreacted along with any reaction by-products.
In a preferred embodiment, a member of the group consisting of SiH2Cl2, SiCl4, Si2Cl6 and SiH4 is used as the first silicon nitride process gas for the silicon nitride thin film deposition process. A substantially inert gas or N2 gas is preferably used as the second silicon nitride process gas and the fourth silicon nitride process gas in this process. In a preferred embodiment, the third silicon nitride process gas used in this process is either NH3 or N2H4 in the form of a gas or as a radical type, or, alternatively, a mixture of N2 and H2 as a mixture of a radical type.
The depositing cycle or process for forming each boron nitride thin film layer comprises the sequential steps of: introducing a first boron nitride process gas containing B to a chamber containing the wafer to be adsorbed on a surface of a previously-formed silicon nitride thin film; introducing a second boron nitride process gas to purge the chamber and to exhaust any of the first boron nitride process gas that remains unadsorbed; introducing a third boron nitride process gas containing a reactive nitrogen entity to the chamber to react with the portion of the first boron nitride process gas that was adsorbed on the surface of the silicon nitride thin film; and, introducing a fourth boron nitride process gas to purge the chamber and to exhaust any of the third boron nitride process gas that remains unreacted along with any reaction by-products.
In a preferred embodiment, a member of the group consisting of BCl3, BBr3, B2H6 and BF3 is used as the first boron nitride process gas for the boron nitride thin film deposition process. A substantially inert gas or N2 gas is preferably used as the second boron nitride process gas and the fourth boron nitride process gas in this process. In a preferred embodiment, the third boron nitride process gas used in this process is either NH3 or N2H4 in the form of a gas or as a radical type, or, alternatively, a mixture of N2 and H2 as a mixture of a radical type.
Other aspects, features and advantages of the present invention are disclosed in the detailed description that follows and by reference to the drawings.